Planned Cost not rolling up to Resource Plan
This was happening due to the customization of the "ResourcePlan" Script Include.
Once reverted, the rollup is working properly.
To do so, follow the steps below.
1. Navigate to System Definition > Script Includes
2. In the "Name" column search for "ResourcePlan" and go to the record
3. In the Versions related list, Right-Click the record with the Source of "System Upgrades: VERSON_NAME..."
4. Select "Revert to this version"
5. Select OK when prompted